Reef chemistry looks intimidating until you realize corals only really ask for two things: stability, and a handful of numbers kept inside sane ranges. You don’t need a chemistry degree. You need a good test kit, a routine, and the discipline not to chase perfection.
The numbers
Salinity: 1.025–1.026 SG, always. Temperature: 77–79°F. Alkalinity: 8–9 dKH — this is the one corals punish you for moving quickly; swings of more than 1 dKH a day stress and strip tissue. Calcium: 400–450 ppm. Magnesium: 1300–1400 ppm — the quiet stabilizer that lets alk and calcium hold hands. Nitrate: 5–15 ppm. Phosphate: 0.03–0.1 ppm. Yes — corals need SOME nutrients. Zero nitrate is starvation, not success.
Test on a schedule, not on a mood
Weekly: alkalinity, nitrate, phosphate, salinity. Every two weeks: calcium, magnesium. Daily glances at temperature. Log every result — the trend matters more than any single reading. A tank drifting from 8.6 to 8.1 dKH over three weeks is telling you something a one-off test never will.
Stability beats perfection
A tank held steady at 7.8 dKH will outperform a tank yo-yoing between 8 and 9.5 every week of the year. Corals adapt to your numbers; they can’t adapt to your swings. Pick targets, get there slowly, and defend them.
When numbers drift
Correct at the speed the problem developed. Alk fell over two weeks? Raise it over days, not hours. High nitrate? Feed smarter and step up water changes before reaching for chemicals. Every additive you dose is a commitment — the simplest system you can maintain consistently is the best system.
Want your water double-checked by people who do this every day? Bring a sample by the shop Friday through Monday — The Underwater Gardener, 2816 N Roosevelt Blvd, Key West. Our Coral Care Guide covers parameter targets for every coral we grow.
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